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The Scientific Method
An organized approach to solve problems.
Steps in the Scientific Method
Observe
Use your five senses
Define the problem
Hypotheses
"Educated guess"
Experiments
Tests each hypothesis to prove/disprove them
Analysis
Compares the results to the original hypothesis
Conclusion (Theory)
A hypothesis supported by experimental evidence
Law
Used to describe a natural phenomenon which has been tested over a long period of time under different conditions.
UNIT 2
Chemistry
The study of matter and the changes it undergoes.
Matter
Anything that has mass and volume (EVERYTHING!)
Mass
The amount of matter in an object (How much “stuff”)
Energy
Anything that can do work or produce heat.
Weight
The force of gravity acting on an object’s mass.
Review: Solids
Liquids
SOLID
Definite shape
Definite volume
Not compressible
High density
LIQUID
Indefinite shape
Definite volume
Not compressible
Less dense than solids
GAS
Indefinite shape
Indefinite volume
Are compressible
Very low density
There are two major areas that matter are classified into
pure substances and mixtures.
Pure Substances
Have uniform and definite composition
Elements
Found on the Periodic Table (approx. 118)
Described by symbols
H
Compounds
Formed when elements chemically combine: H2O
Mixtures
Two or more pure substances physically mixed together.
In compounds
the elements are bonded to each other. In mixtures
No definite composition – cannot assign a fixed ratio (ex: H2O)
Two Types of Mixtures
Heterogeneous mixtures
Does not have a uniform composition. Parts of the mixture can be physically seen and “picked out” of the mixture. Examples: Cereal
Homogeneous mixtures
Has a uniform composition. Parts of the mixture cannot be “picked out”. Examples: sugar water
Pure Substances
Pure substances have a unique set of chemical and physical properties.
Physical Properties
Properties that can be measured or observed without changing the identity (or composition) of a substance.
The chemical make-up is not changing when these properties are observed!
Examples: color
odor
Chemical Properties
Properties that indicate how a substance reacts with other substances.
These properties are only observed when the substance undergoes a chemical change.
Examples: flammable
combustible
Physical Changes
Changes in appearance without changing composition.
Examples: cutting
breaking
Changes in state such as: melting
freezing
Chemical Changes (Reactions)
One or more substances react to form new substances with different chemical and physical properties.
The beginning substance is different than the ending substance.
Examples: Rusting
burning
Chemical Changes (cont.)
All chemical reactions can be described by a chemical equation.
Reactants 🡪 Products
Iron + Oxygen 🡪 Iron (III) Oxide
Fe + O2 🡪 Fe2O3
(Formula Equation)
(Word Equation)
“yields”
Law of Conservation of Mass
In any chemical or physical change
matter cannot be created or destroyed.
Mass Reactants = Mass Products
Hydrogen + Oxygen 🡪 Water
10 grams + 5 grams
Accuracy
How close a measurement is to the true or accepted value
Precision
How close multiple measurements are to each other
Two new conversion factors you must know
1 inch = 2.54cm and 1 mile = 5
280ft
UNIT
DEMOCRITUS (400 B.C)
A Greek philosopher
Was the first person to think about an atom’s existence.
Believed that matter was composed of tiny indivisible particles called atoms.
He had no experimental evidence to support his thoughts.
John Dalton (1766-1844)
A meteorologist
Unlike Democritus
he had experimental evidence to support his theory.
Dalton had four major points (postulates) to his theory.
DALTON’S THEORY
All elements are composed of indivisible particles called atoms.
Atoms of the same element are identical. The atoms of any one element are different from those of another.
Atoms of different elements mix or combine in whole number ratios.
Chemical reactions occur when atoms separate
join
In a chemical reaction
atoms of one element NEVER change into another.
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